This invention relates to a method of dispersing a catalytic agent into an underground mineral deposit in order to facilitate the generation of synthetic fuels. More specifically, this invenion relates to the dispersion of catalysts with explosives for in situ mining of carbonaceous minerals.
Although many methods of in situ mining of carbonaceous minerals are patented, none teach the use of a catalyst to enhance recovery. The most general technique for in situ mining, as applied to oil shale, comprises the use of a retorting process. In this process, a retorting zone is formed by mining an access tunnel to or near the retorting area and then removing a portion of the oil shale deposit by conventional mining techniques. About 5 to about 40 percent, preferably about 15 to about 25 percent, of the oil shale in the retorting area is removed to provide void space in the retorting area. The oil shale in the retorting area is then rubblized by well-known mining techniques to provide a retort zone containing rubblized shale. One specific method for forming this underground retort is to undercut the mineral deposit and remove a portion of it in order to provide a cavity. Drill holes are then drilled at various angles and depths into the oil shale surrounding the cavity. Into these drill holes explosives are placed and detonated in order to rubblize the oil shale, preferably forming an area of rubble having a particle size less than 4 feet in diameter. Several of the techniques employed to form the underground cavity and rubblized area are: sublevel stoping, sublevel caving, and room and pillar mining. After the underground retort is formed, the zone of rubblized oil shale is subjected to a retorting process. In such a process, hot gases are passed through the rubblized particles to effectively form and remove liquid hydrocarbons from the oil shale. This is commonly done by passing a retorting gas such as air or air mixed with steam and/or hydrocarbons through the deposit. Most commonly, air is pumped into one end of the retort and a fire or flame front initiated. This flame front is then passed slowly through the rubblized deposit to effect the retorting. Not only is shale oil effectively produced, but also a mixture of off-gases from the retorting is also formed. These gases contain carbon monoxide, nitrogen, ammonia, carbon dioxide, hydrogen sulfide, carbonyl sulfide, and oxides of sulfur and nitrogen. Generally, a mixture of off-gases, water, and shale oil are recovered from the retort. The carbonaceous product is then subject to standard refinery operations to produce a usable product.
Oil shale can be found in various places throughout the world, expecially in the United States in such states as Colorado, Utah and Wyoming. Some especially important deposits can be found in the Green River formation in Piceance Basin, Garfield and Rio Blanco counties, and northwestern Colorado.
The word "catalyst" refers to any substances of which a fractionally small percentage strongly affects the rate of a chemical reaction. For purposes of this invention, the word "catalyst" refers to substances which in relatively small amounts lead to increased yields or rates of formation of desirable products and decreased yields or rates of formation of undesirable products. Though the catalyst itself usually undergoes no chemical change, it is often altered physically by chemically adsorbed molecules of the reactants. Most catalysts accelerate the rate of reaction, but a few retard it. Catalysts may be solid, liquid, or gaseous and their life cycle varies depending on process conditions, after which it must be regenerated or replaced. Catalysts, one of the most important phenomena in nature, is the "loosening" of the chemical bonds of one or more reactants by another substance (catalyst) in such a way that a fractionally small percentage of the catalyst can greatly accelerate the rate of the reaction while remaining unconsumed. Thus one part by volume of catalyst can activate thousands of parts of reactants. A familiar example is the oxidation of iron which is catalyzed by atmospheric water vapor.
Most catalysts are highly specific in their application, for example: powdered nickel is particularly effective for hydrogenation and group VIII metals for the conversion of straight-chain to cyclic hydrocarbons. The activity of a catalyst can be increased by adding promoters which serve to increase the surface area, for example, by increasing porosity. Although catalysts usually increase reactivity, it is possible to catalystically decelerate undesirable reactions by dispersing catalysts (poisons) that would poison naturally occurring catalysts. Another way to decelerate a reaction is to introduce catalysts into the carbonaceous material which would favor competing reactions, thereby minimizing the undesirable kind.
The term "explosive" refers to a chemical compound, usually containing nitrogen, that detonates as a result of shock or heat. Dynamite was the most widely used explosive for blasting purposes until 1955, when it was largely replaced by prills-and-oil and slurry types. The former consist of 94 percent ammonium nitrate prills and 6 percent fuel oils. Slurry blasting agents are based on thickened or gelatinized ammonium nitrate slurries sensitized with TNT (2,4,6-trinitrotoluene), other solid explosives, or aluminum. It is the most efficient commercial blasting agent now in use. Because high explosives vary greatly in their shock sensitivity, it is possible to select an explosive to satisfy any particular need. The range encompasses such explosives as mercury fulminate and nitroglycerin, which are the most sensitive, to TNT and ammonium nitrate which are comparatively difficult to detonate, and usually require an activating device such as blasting caps to set them off.
A number of patents describe methods of in situ mining of carbonaceous deposits, especially oil shale and the most relevant ones are hereinafter described.
Garret, U.S. Pat. No. 3,661,423, is directed to the recovery of carbonaceous values by in situ retorting of rubblized deposits such as oil shale. A limited undercut is made over a large area leaving an overlaying deposit supported by a multiplicity of pillars. The pillars are then removed and the overlaying deposit expanded to fill the void with particles of uniform size, porosity and permeability. Communication is then established with the upper level of the expanded deposit and a high temperature gaseous media which will liquefy or vaporize the carbonaceous values is introduced in a manner which causes the released values to flow downward for collection at the base of the expanded deposit. Convenient media are hot flue gases created by igniting the upper level of the expanded carbonaceous deposit forcing a flow of hot gases downward through the expanded deposit.
Van Poollen, U.S. Pat. No. 3,001,776, is directed to the in situ retorting of oil shale and teaches that the retorts can be formed by well-known mining practices which may include sublevel stoping, shrinkage stopes, sublevel caving or block caving. An access shaft is mined with various drifts so that the retorting area can be worked at a plurality of levels. The overlaying oil shale above a stope is fractured, generally by explosives detonated in blast holes in the overhead deposit. Some of the oil shale is removed to achieve the desired porosity. The retort filled with rubble can be retorted in either the upflow or downflow direction by the injection of air. Ignition can be accomplished by any suitable method such as oxygen used in conjunction with natural gas.
Ellington, U.S. Pat. No. 3,586,377, is directed to a method of in situ recovery of shale oil. The method of obtaining shale oil from a zone of unmined oil shale comprises establishing access means at least two points in said zone, establishing communication between these access means through the zone, fragmenting at least part of the oil shale in the zone in the area of the communication to produce a porous mass of fragmented oil shale, supplying heating means to said fragmented oil shale through one of said access points, to pyrolyze shale oil in the oil shale and collecting said shale oil through the other of said access means.
Prats, U.S. Pat. No. 3,434,757, is directed to a method of in situ recovery of shale oil wherein the rubblized oil shale is created by forming at least two tunnels, exploding the archways between the tunnels and thereby creating a large roof which collapses. Another series of explosives extending radially upward and substantially parallel to the tunnels is detonated to rubblize the overlaying oil shale. Hot fluid is then circulated through the permeable mass of oil shale to release the shale oil.
Ridley, U.S. Pat. No. 3,951,456, discloses an in situ process for recovering carbonaceous values from a subterranean deposit comprising the steps of (a) developing an in situ rubble pile within a retorting chamber of a subterranean carbonaceous deposit having a retorting fluid entrance and retorting fluid exit, said rubble pile being formed by undercutting at about the base of the carbonaceous deposit to remove a predetermined volume of material and form a sloped floor having a high point at the shortest retorting fluid path between the retorting fluid entrance and the floor and the low point at the periphery of the floor and expanding the deposit to form the in situ rubble pile wherein the bulk permeability of the rubble pile increases from the shortest retorting fluid path to the longest retorting fluid path between the retorting fluid entrance and the retorting fluid exit so that the resistance to retorting fluid flow through the rubble pile along all retorting fluid paths is approximately equal; (b) establishing the retorting fluid entrance between the rubble pile and a source of retorting fluid; (c) establishing the retorting fluid exit between the rubble pile and a destination for the retorting fluid, the exit communication with the rubble pile being spaced by at least a portion of the rubble pile from the retorting fluid entrance; (d) retorting the rubble pile to extract the carbonaceous values therefrom, the retorting step including the passage of the retorting fluid through the rubble pile along the retorting fluid paths; and (e) recovering the retorted carbonaceous values.
It is an object of this invention to provide a method of in situ mining of carbonaceous mineral deposits whereby an explosive charge is used to fracture and rubblize the mineral as well as disperse a catalyst.
It is an object of this invention to provide a process for generating synthetic fuels from carbonaceous minerals by employing a catalyst to accelerate, decelerate or otherwise control the step in which hydrocarbon values are recovered from the mineral.
It is further an object of this invention to increase the yield of the recoverable product.
It is still further an object of this invention to obtain a better quality product.